Method for operating a mobile radiotelephone network

ABSTRACT

A method is proposed for operating a mobile radio network ( 1 ), which permits an error-free exchange of packet data units in the event of a connection change ( 700 ) between a mobile unit ( 10 ) and superordinate network units ( 50, 55 ). In this context, useful data is transmitted in the mobile radio network ( 1 ) between the mobile unit ( 10 ) and a first radio base station ( 25 ), the useful data being combined to form packet data units prior to its transmission. For the transmission of the packet data units, transmission-specific information describing an instantaneous state of the transmission is stored both in the mobile unit ( 10 ) and in a first network unit ( 50 ) superordinate to the first radio base station ( 25 ). In response to the connection change ( 700 ) of the mobile unit ( 10 ) from the first radio base station ( 25 ) to a second radio base station ( 30 ) having a second superordinate network unit ( 55 ), the transmission-specific information stored in the first superordinate network unit ( 50 ) is transmitted to the second superordinate network unit ( 55 ) in order to continue the transmission after the connection change essentially directly from its instantaneous state. Prior to the connection change ( 700 ), the transmission of the packet data units from the first radio base station ( 25 ) to the mobile unit ( 10 ) is halted by the first superordinate network unit ( 50 ). With the transmission-specific information from the first superordinate network unit ( 50 ), a first identifier of the packet-data unit expected as next from the mobile unit ( 10 ) in the first superordinate network unit ( 50 ) is transmitted to the second superordinate network unit ( 55 ). A first connection-change packet data unit which includes the first identifier is sent by the second superordinate network unit ( 55 ) to the mobile unit ( 10 ).

BACKGROUND INFORMATION

[0001] The present invention is based on a method for operating a mobile radio network according to the species defined in the main claim.

[0002] From the not yet pre-published German patent application having the file no. 19956062.5, a method is already known for operating a mobile radio network, in which useful data is transmitted between a mobile unit and a first radio base station, the useful data being combined to form packet data units prior to its transmission; for the transmission of the packet data units, transmission-specific information which describes an instantaneous state of the transmission is stored both in the mobile unit and in a first network unit superordinate to the first radio base station, and in the event of a connection change of the mobile unit from the first radio base station to a second radio base station having a second superordinate network unit, the transmission-specific information stored in the first superordinate network unit is transmitted to the second superordinate network unit in order to continue the transmission after the connection change essentially directly from its instantaneous state.

SUMMARY OF THE INVENTION

[0003] In contrast, the method of the present invention having the features of the main claim has the advantage that the transmission of the packet data units from the first radio base station to the mobile unit is halted by the first superordinate network unit prior to the connection change; that with the transmission-specific information of the first superordinate network unit, a first identifier of the packet data unit expected as next from the mobile unit in the first superordinate network unit is transmitted to the second superordinate network unit; and that a first connection-change packet data unit which includes the first identifier is transmitted from the second superordinate network unit to the mobile unit. This ensures that no packet data units are transmitted to the mobile unit during the connection change, in order to prevent a faulty detection of such packet data units because of a possible reconfiguring or resetting of the mobile unit. Furthermore, the first connection-change packet data unit ensures that after the connection change, the mobile unit continues the sending with the packet data unit expected by the second superordinate network unit, so that no packet data units sent during the connection change from the mobile unit to the first or the second superordinate network unit become lost, for example, because of a faulty reception or a faulty evaluation. Rather, a continuous reception, unimpaired by the reconfiguration or resetting processes possibly to be carried out during the connection change, of the packet data units sent by the mobile unit is ensured in the second superordinate network unit.

[0004] A further advantage is that the first identifier is sent by using a packet data unit formed as a connection-change packet data unit, so that it may be transmitted efficiently to the mobile unit via the existing data channels without additional signaling and without setting up and tearing down new data channels or reconfiguring existing data channels.

[0005] Advantageous further refinements and improvements of the method indicated in the main claim are rendered possible by the measures specified in the dependent claims.

[0006] It is particularly advantageous that the sending of packet data units is halted by the mobile unit after receiving the first identifier. In this way, the mobile unit is informed about the connection change and is prevented from sending further packet data units which are possibly really not yet expected by the second superordinate network unit.

[0007] It is also advantageous that, after reception of the first identifier, the mobile unit transmits to the second superordinate network unit a second connection-change packet data unit which includes a second identifier of the packet data unit expected as next in the mobile unit from the second superordinate network unit. This ensures that the sending of packet data units may be commenced again by the second superordinate network unit at the earliest possible moment after the connection change, namely, when the mobile unit has communicated by the second identifier that it is ready to receive these packet data units.

[0008] A further advantage is that the second connection-change packet data unit is transmitted from the mobile unit to the second superordinate network unit after reconfiguration or resetting of the mobile unit.

[0009] The reconfiguration or resetting of the mobile unit after reception of the first identifier ensures that all packet data units which were still sent by the first superordinate network unit are received with the mobile unit not reconfigured or reset, and that all packet data units which are received from the second superordinate network unit are detected with the mobile unit reconfigured or reset.

[0010] Another advantage is that packet data units are ignored by the second superordinate network unit which are received after the connection change and prior to receiving the second connection-change packet data unit from the mobile unit. This prevents packet data units, which the mobile unit had still sent prior to the connection change but which were only received in the second superordinate network unit after the connection change, from leading to a faulty detection in the second superordinate network unit because, for example, the connection change induced a reconfiguration or a resetting of the second superordinate network unit. Thus, a reception, unimpaired by the reconfiguration or resetting processes possibly to be carried out in response to the connection change, of the packet data units sent-by the mobile unit is ensured in the second superordinate network unit.

[0011] A further advantage is yielded in that the sending of packet data units from the mobile unit after reconfiguration or resetting of the mobile unit is continued with the packet data unit referenced by the first indicator, it and the following packet data units being transmitted to the second superordinate network unit. This ensures that the mobile unit continues the data transmission after the connection change with packet data units adapted to the new connection to the second superordinate network unit, so that these packet data units can also be detected in the second superordinate network unit.

[0012] Another advantage is yielded in that the second superordinate network unit is initialized prior to reception of the transmission-specific information. This prevents the transmission-specific information from not being understood by the second superordinate network unit because of a lack of initialization.

[0013] It is also advantageous that the first identifier in the first connection-change packet data unit and/or the second identifier in the second connection-change packet data unit is in each case transmitted as a sequence number of the packet data unit expected as next. In this way, only insignificant bandwidth is used for transmitting the individual connection-change packet data units, particularly when the sequence number uses only 8 bits.

BRIEF DESCRIPTION OF THE DRAWING

[0014] An exemplary embodiment of the present invention is shown in the drawing, and explained in detail in the following description.

[0015]FIG. 1 shows a block diagram of a mobile radio network;

[0016]FIG. 2 shows a block diagram for a connection between a mobile unit and a first superordinate network unit via a first radio base station prior to a connection change;

[0017]FIG. 3 shows a block diagram for a connection between the mobile unit and a second superordinate network unit via a second radio base station after a connection change;

[0018]FIG. 4 shows an example for a time sequence of the connection change according to the related art; and

[0019]FIG. 5 shows an example for a time sequence of the connection change according to the present invention.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

[0020] The present invention deals with a method for operating a mobile radio network 1 according to FIG. 1, in which during a set-up connection, a connection change is carried out between two radio base stations 25, 30, which is also designated as “relocation”. In this context, mobile radio network 1 may be set up, for example, according to the GSM standard (Global System for Mobile Communications) or according to the UMTS standard (Universal Mobile Telecommunications System). The method relates especially to the sending of transmission-specific information of the set-up connection, for example, in the form of internal protocol information of a convergence protocol layer 130, 135 between two superordinate network units 50, 55 of cellular mobile radio network 1.

[0021] Cellular mobile radio network 1 is made of various units 10, 20, 25, 30, 35, 50, 55, 60 which are physically interconnected. In this context, 10 designates a mobile unit of mobile radio network 1 which, for example, may be designed as a mobile telecommunications terminal. Mobile telecommunications terminal 10 is connected to a first radio base station 25 of mobile radio network 1 via a first air interface 90. First radio base station 25 is connected to a first superordinate network unit 50 via a first fixed-network connection 81. A second radio base station 30 is connected to a second superordinate network unit 55 via a second fixed-network connection 82. A third radio base station 20 is connected to first superordinate network unit 50 via a third fixed-network connection 80. A fourth radio base station 35 is connected to second superordinate network unit 55 via a fourth fixed-network connection 83. First superordinate network unit 50 is connected to a highest network unit 60 via a fifth fixed-network connection 85. Second superordinate network unit 55 is connected to highest network unit 60 via a sixth fixed-network connection 86. Optionally, first superordinate network unit 50 may be connected to second superordinate network unit 55 via a seventh fixed-network connection, as shown by a dotted line in FIG. 1. According to the UMTS standard, first superordinate network unit 50, second superordinate network unit 55 and possibly further superordinate network units form so-called Radio Network Subsystems (RNS). According to the UMTS standard, the highest network unit forms a so-called GPRS Support Node (General Packet Radio System Support Node) (GSN).

[0022] Logical connections are produced in cellular mobile radio network 1 for transmitting data between mobile telecommunications terminal 10 and the remaining units of mobile radio network 1 involved in the set-up connection. In this context, various types of logical connections between mobile telecommunications terminal 10 and the various participant units of mobile radio network 1 exist simultaneously. These logical connections originate from a hierarchical model in which each hierarchical layer corresponds to a protocol that is present both in mobile telecommunications terminal 10 and in the corresponding unit of mobile radio network 1, and that implements the corresponding logical connection.

[0023]FIG. 2 shows, by way of example, the logical connections between mobile unit 10 and first superordinate network unit 50, as well as between mobile unit 10 and first radio base station 25. The lowest hierarchical layer in this hierarchical model is formed by a first physical layer 110 in mobile telecommunications terminal 10 and a second physical layer 115 in first radio base station 25, which implement a physical connection, corresponding to first air interface 90, between mobile telecommunications terminal 10 and first radio base station 25 of mobile radio network 1. Above it is a data-protection layer which, according to the UMTS standard, is also designated as Data Link Layer, and which is divided into a plurality of sublayers and implements various logical connections between mobile telecommunications terminal 10 and first superordinate network unit 50 designated as Radio Network Controller (RNC) according to the UMTS standard. According to the UMTS standard, such a sublayer is the Radio Link Control layer (RLC), in which a first RLC protocol 120 in mobile telecommunications terminal 10 and a second RLC protocol 125 in first superordinate network unit 50 implement a first logical RLC connection 101 as one of the indicated logical connections. Another sublayer is the Packet Data Convergence Protocol layer (PDCP) as designated according to the UMTS standard, in which a first PDCP protocol 130 in mobile telecommunications terminal 10 and a second PDCP protocol 135 in first superordinate network unit 55 implement a first logical PDCP connection 102. In the higher hierarchical layers, such as the network and transport layer, further protocols, e.g., the Radio Resource Control Protocol RRC, the Internet Protocol IP, the Transit Control Protocol TCP and the like may build up further logical connections. According to FIG. 2, adjacent layers in the hierarchical model are interconnected, superordinate layers enlisting the service of correspondingly adjacent subordinate layers. As indicated in FIG. 1, second physical layer 115 is connected via the first fixed-network connection to first superordinate network unit 50, and is connected there to second RLC protocol 125.

[0024] The publication “Technical Specification 25.301, UMTS Radio Interface Protocol Architecture” describes the corresponding UMTS protocol architecture of so-called layers 2 and 3, to which also belongs the packet data convergence protocol layer. In particular, the packet data convergence protocol layer and its position within this architecture are known. PDCP protocol 130, 135 is known from the publication “Technical Specification 25.323, Packet Data Convergence Protocol”, in so far as it is specified till now.

[0025] One task of PDCP protocol 130, 135 is the compression of packet data control information which was added by the protocols of the transport and network layer, situated above the packet data convergence protocol layer, to the useful data—likewise combined in the packet data protocol layer prior to its transmission to form data units or packet data units—of an application likewise operating above the packet data convergence protocol layer, and which must be compressed prior to transmission via first air interface 90, in order to permit an efficient transmission.

[0026] The cellular mobile radio network offers the possibility of data transmission from mobile telecommunications terminal 10 to a unit of mobile radio network 1 even when the user of mobile telecommunications terminal 10 leaves the radio cell covered by first radio base station 25. To that end, a method is carried out between mobile telecommunications terminal 10 and mobile radio network 1 for transferring the set-up connection for the data transmission from first radio base station 25 to second radio base station 30, provided that the user of mobile telecommunications terminal 10 moves into the radio cell covered by second radio base station 30. This connection change as described is also designated as “handover” between the radio base stations.

[0027] In the case of a connection change, it may now be that second radio base station 30, to which the connection should be handed over, is connected to a different superordinate network unit than previous first radio base station 25. This is the case in the exemplary embodiment described, according to which second radio base station 30, in contrast to first radio base station 25, is connected to second superordinate network unit 55. Therefore, simultaneously with or after the connection handover from a first radio base station to a second, the connection handover between first superordinate network unit 50 and second superordinate network unit 55 is also carried out. This connection handover is called “relocation” between the network units.

[0028] Each protocol always exists at least twice on the same protocol layer plane in different network units, as also in FIG. 2, the RLC protocol and the PDCP protocol exist both in mobile telecommunications terminal 10 and in first superordinate network unit 50. Especially PDCP protocols 130, 135, according to the UMTS standard as described, exist first of all in mobile telecommunications terminal 10 and secondly in first superordinate network unit 50, as well as in further superordinate network units, which are formed as RNC. In the case of the connection change described, the existing data connection between mobile telecommunications terminal 10 and mobile radio network 1 is routed in such a way that it runs via second radio base station 30 and second superordinate network unit 55. Consequently, prior to the connection change, first PDCP protocol 130 in mobile telecommunications terminal 10 transmits to second PDCP protocol 135 in first superordinate network unit 55 via first logical PDCP connection 102, and after the connection change, to a third PDCP protocol 136 of second superordinate network unit 55 according to FIG. 3.

[0029] The present invention now starts out from the specific and exemplary scenario that mobile telecommunications terminal 10 is connected to units of mobile radio network 1, such as first radio base station 25, first superordinate network unit 55 and highest network unit 60 via the necessary physical and logical connections, particularly first logical PDCP connection 102 between mobile telecommunications terminal 10 and first superordinate network unit 50 implemented by first PDCP protocol 130 and second PDCP protocol 135, and a data transfer, thus an exchange of packet data units takes place via these connections.

[0030] In this context, first PDCP protocol 130 and second PDCP protocol 135 store transmission-specific information on the basis of its functionality which is necessary for compressing and manipulating the useful data and the packet-data control information. To permit correct functioning of both PDCP protocols 130, 135 indicated, a portion of this transmission-specific information must be synchronized or even identical in both PDCP protocols 130, 135. If mobile telecommunications terminal 10 now changes the radio cell in mobile radio network 1 into a new radio-cell, for example, because of a movement of mobile telecommunications terminal 10 out of the transmission range of first radio base station 25, then a connection change is carried out and a new physical connection is set up between mobile telecommunications terminal 10 and second radio base station 30 which covers the new radio cell. In this case, the new physical connection corresponds to a second air interface 91 according to FIG. 1 and FIG. 3. FIG. 3 shows the connection of mobile telecommunications terminal 10 to second superordinate network unit 55 via second radio base station 30, the same reference numerals identifying the same elements as in FIG. 2. In this context, second radio base station 30 according to FIG. 3 is connected via second fixed-network connection 82 to second superordinate network unit 55, i.e., its RLC protocol, which here is designated as third RLC protocol 126. Second superordinate network unit 55 is set up like first superordinate network unit 50, and in corresponding manner, has third PDCP protocol 136 in addition to third RLC protocol 126. Second radio base network 30 is connected in mobile radio network 1, as described, to second superordinate network unit 55 different from first superordinate network unit 50. Thus, the logical connections between mobile telecommunications terminal 10 and second superordinate network unit 55 are also newly set up. In so doing, a second logical RLC connection 103 is set up between first RLC protocol 120 and third RLC protocol 126. A second logical PDCP connection 104 is set up between first PDCP protocol 130 and third PDCP protocol 136. Thus, first logical PDCP connection 103 is replaced by second logical PDCP connection 104. Moreover, third PDCP protocol 136 must first be newly produced in second superordinate network unit 55 after the connection change.

[0031] To now permit a correct data flow via second logical PDCP connection 104, first of all, first PDCP protocol 130 in mobile telecommunications terminal 10 and third PDCP protocol 136 in second superordinate network unit 55 must again be synchronized. One method for this is the resetting of first PDCP protocol 130 in mobile telecommunications terminal 10 into a defined output state which corresponds to the output state of third PDCP protocol 136 newly produced in response to the connection change, first PDCP protocol 130 and third PDCP protocol 136 then containing the same transmission-specific information.

[0032] If, in the course of an existing mobile radio link between mobile unit 10 and mobile radio network 1, the superordinate network unit, via which the mobile radio link runs, changes, then second RLC protocol unit 2200 provided for producing second RLC protocol 125 and second PDCP protocol unit 2100 provided for producing second PDCP protocol 135 are erased in original, first, superordinate network unit 50, and a third RLC protocol unit 3200 and a third PDCP protocol unit 3100 are set up and configured in such a way in new, second, superordinate network unit 55 that subsequently a data transmission between third RLC protocol unit 3200 and first RLC protocol unit 1200 provided for producing first RLC protocol 120, or between third PDCP protocol unit 3100 and first PDCP protocol unit 1100 provided for producing first PDCP protocol 130, thus between third RLC protocol 126 and first RLC protocol 120 or between third PDCP protocol 136 and first PDCP protocol 130 according to FIGS. 4 and 5 is possible. To be able to guarantee a loss-free data transmission by PDCP protocol units 1100, 2100, 3100 in the case of such a connection change designated as “relocation”, for reasons connected with the compression of the data, they must store and number the packet data units received from higher protocol layers. The packet data units are only erased from the memory, provided for this purpose and not shown in the Figures, when their error-free transmission has been acknowledged by the respective receiving RLC protocol unit. In this context, the method known at present from the publication “Packet Data Convergence (PDCP) Protocol”, 3GPP, Technical Specification 25.323 is described in the following:

[0033] During the data transmission, each packet data unit received from a higher protocol layer for the data transmission is numbered with the aid of a so-called PDCP send sequence number and stored by corresponding PDCP protocol unit 1100, 2100, 3100 of the respective transmitter. After that, the packet data unit is optionally compressed and handed over to the RLC protocol layer for the transmission. In corresponding PDCP protocol unit 1100, 2100, 3100 of the respective receiver, each packet data unit received by the RLC protocol layer there is likewise counted, with the giving of a PDCP receive sequence number. Since the RLC protocol layer guarantees a loss-free transmission of the packet data units in the proper sequence, the PDCP send sequence number and the PDCP receive sequence number of each transmitted data packet correspond. Since mobile unit 10 and respective superordinate network units 50, 55 are each able to function both as transmitter and as receiver, they as a rule include PDCP protocol units 1100, 2100, 3100 both for transmitting and for receiving packet data units. Therefore, there are PDCP send sequence numbers and PDCP receive sequence numbers both in the uplink, i.e. in the transmission link from mobile unit 10 to relevant superordinate network unit 50, 55, as well as in the downlink, i.e. in the transmission link from relevant superordinate network unit 50, 55 to mobile unit 10. Thus, mobile unit 10 counts the transmitted packet data units with the so-called PDCP uplink send sequence number, and the received packet data units with the PDCP downlink receive sequence number. Relevant superordinate network unit 50, 55 then counts the transmitted packet data units with the so-called PDCP downlink send sequence number, and the received packet data units with the PDCP uplink receive sequence number.

[0034] If, at this point, a connection change occurs, then first superordinate network unit 50 transmits the following transmission-specific information to second, new superordinate network unit 55:

[0035] 1) the PDCP-uplink receive sequence number of the next expected data packet to be received by second superordinate network unit 55, and

[0036] 2) the packet data units still stored in its memory and the PDCP-downlink send sequence number of the stored packet-data unit which would have been transmitted as the next to mobile unit 10, as-well as the PDCP-downlink send sequence numbers of all packet data units stored for this purpose, they being stored in the sequence in which they were received from the higher protocol layers.

[0037] Second superordinate network unit 55 now sends the PDCP-uplink receive sequence number of the next data packet expected and to be received by second superordinate network unit 55 to mobile unit 10. Mobile unit 10 in turn sends the PDCP-downlink receive sequence number of the next packet data unit expected and to be received by mobile unit 10 to second superordinate network unit 55. In this way, respective PDCP protocol units 1100, 2100, 3100, responsible for the transmitting, in mobile unit 10 and in relevant superordinate network unit 50, 55 know which packet data units were correctly received by respective PDCP protocol unit 1100, 2100, 3100, responsible for the reception in mobile unit 10 and in relevant superordinate network unit 50, 55 prior to the connection change, and from which packet data unit it is necessary to begin again in the useful-data transfer after the connection change.

[0038] As indicated, the method described above is known from the publication “Packet Data Convergence (PDCP) Protocol”, 3GPP, Technical Specification 25.323. The manner in which PDCP protocol units 1100, 2100, 3100, i.e. the manner in which mobile unit 10 and relevant superordinate network unit 50, 55 behave when a connection change takes place, and how the above-described exchange of the PDCP-downlink receive sequence number and the PDCP-uplink receive sequence number, respectively, expected as the next, between mobile unit 10 and second superordinate network unit 55 is carried out is not described in greater detail.

[0039] It is conceivable here to transmit this transmission-specific information through other than PDCP protocol 130, 135, 136, for example, through Radio Resource Control protocol RRC, which also receives and processes the message about the occurrence of a connection change, or through PDCP protocol 130, 135, 136 itself. The transmission channels used for transmitting the packet data units are also not stipulated.

[0040] Formats for the packet data units (PDCP-PDUs) sent by the respective PDCP protocol layer to the respective subordinate RLC protocol layer are likewise known from the publication “Packet Data Convergence (PDCP) Protocol”, 3GPP, Technical Specification 25.323. Under the state of the art, the “PDCP-No-Header-PDU” and the “PDCP-Data-PDU” are defined in the cited publication “Packet Data Convergence (PDCP) Protocol”.

[0041] According to FIG. 4, the following problems may occur when working with the method described:

[0042] Problem 1:

[0043] If PDCP protocol unit 1100 in mobile unit 10 has handed over first packet data units 510 to RLC protocol unit 1200 in mobile unit 10 prior to a first occurring connection change 500, and, for example, because of a first transmission error 520 prior to first connection change 500, RLC protocol unit 1200 of mobile unit 10 then first sends these packet data units to RLC protocol unit 3200 of second superordinate network unit 55 after first connection change 500 according to transmission step 521 in FIG. 4, then RLC protocol unit 3200 of second superordinate network unit 55 is only able to hand over the received packet data units according to transmission step 530 to PDCP protocol unit 3100 of second superordinate network unit 55 after first connection change 500. These packet data units thus received may then possibly not be properly treated, e.g. decompressed, by PDCP protocol unit 3100 of second superordinate network unit 55, since during or after first connection change 500, the type of data manipulation in PDCP protocol unit 3100 of second superordinate network unit 55 may have changed compared to PDCP protocol unit 2100 of first superordinate network unit 50 due to a first re-setting process 540 of PDCP protocol unit 3100 of second superordinate network unit 55 directly after first connection change 500; first re-setting process 540 may be, for example, the re-setting of the compression algorithm in response to the initialization of PDCP protocol unit 3100 of second superordinate network unit 55.

[0044] Problem 2:

[0045] If, prior to a second occurring connection change 600, PDCP protocol unit 2100 in first superordinate network unit 50 has handed over second packet data units 610 to RLC protocol unit 2200 of first superordinate network unit 50, and, for example, because of a second transmission error 620 prior to second connection change 600, RLC protocol unit 1200 of first superordinate network unit 50 then first sends these packet data units to RLC protocol unit 1200 of mobile unit 10 after second connection change 600 according to transmission step 621 in FIG. 4, then RLC protocol unit 1200 of mobile unit 10 is only able to hand over the received packet data units according to transmission step 630 to PDCP protocol unit 1100 of mobile unit 10 after second connection change 600. These packet data units thus received may then possibly not be properly treated, e.g. decompressed, by PDCP protocol unit 1100 of mobile unit 10, since after second connection change 600, the type of data manipulation in PDCP protocol unit 1100 of mobile unit 10 may have changed due to a second re-setting process 640 of PDCP protocol unit 1100 of mobile unit 10 directly after second connection change 600; second re-setting process 640 may be, for example, the re-setting of the compression algorithm in PDCP protocol unit 1100 of mobile unit 10.

[0046] According to the present invention, the following is proposed for solving the addressed problems:

[0047] To permit an exchange of PDCP receive sequence numbers between mobile unit 10 and second superordinate network unit 55 in general, first of all a new format for a PDCP packet data unit (PDCP-PDU) is proposed which essentially contains a PDCP sequence number and is designated in the following as connection-change packet data unit or as PDCP sequence-number packet data unit (PDCP-SNPDU). To be able to distinguish the PDCP-SNPDU from the packet data units already defined and described in the related art upon reception, the PDCP-SNPDU proposed here also contains the information element “PDU type”, known from the related art and used in the packet data units utilized for the transmission of the useful data, which in the PDCP-SNPDU contains a value including three bits, for example 001, specific for the PDCP-SNPDU. Moreover, the PDCP-SNPDU contains an information element R that includes 5 bits and by which the length of the PDCP-SNPDU is expanded to a value divisible by 8. This information element may assume any values; it may in particular be used for further signalings irrelevant for this invention. It is not ruled out to add still further information elements to this PDCP-SNPDU; however, according to the present invention, only the information elements PDU type, R and PDCP sequence number are of importance in the PDCP-SNPDU. The table shows the proposed PDCP-SNPDU format in terms of an example having an 8-bit PDCP sequence number, a 3-bit PDU type information element and a 5-bit information element R: TABLE PDCP-SNPDU Bit 8 7 6 5 4 3 2 1 Oct 1 PDU type R Oct 2 PDCP sequence number

[0048] The PDCP-SNPDU according to the table includes two octets, each made of 8 bits.

[0049] The method of the present invention now includes the following steps shown in FIG. 5:

[0050] Since the connection change is always started from the network, particularly from highest network unit 60, the network always begins with the first step. The normal data exchange of packet data units between mobile unit 10 and first superordinate network unit 50 is designated prior to a third connection change 700 in FIG. 5 by reference numeral 701.

[0051] In the following, the sequence after third connection change 700 is described.

[0052] Step 1:

[0053] PDCP protocol unit 2100 in first superordinate network unit 50 stops the data transmission via the hitherto used transmission channels to mobile unit 10.

[0054] Step 2:

[0055] PDCP protocol unit 2100 in first superordinate network unit 50 transmits transmission-specific information 730, indicated in the publication “Packet Data Convergence (PDCP) Protocol”, to PDCP protocol unit 3100 of second superordinate network unit 55. Among this is the PDCP-uplink receive sequence number of the packet data unit expected as next in first superordinate network unit 50, and the memory contents having the PDCP-downlink send sequence numbers of the packet data units stored for sending to mobile unit 10.

[0056] Step 3:

[0057] PDCP protocol unit 3100 of second superordinate network unit 55 sends the PDCP-uplink receive sequence number of the next expected packet data unit via RLC protocol unit 3200 of second superordinate network unit 55 according to transmission step 740 and RLC protocol unit 1200 of mobile unit 10 according to transmission step 741 to PDCP protocol unit 1100 of mobile unit 10 according to transmission step 742, in that it generates a PDCP-SNPDU, for example, according to the table, sets the information element there according to the PDCP-uplink receive sequence number to be sent, and hands over the PDCP-SNPDU to identical RLC protocol unit 3200 of second superordinate network unit 55, and thus to the identical logical channel, namely, second logical RLC connection 103 for the error-free transmission in the correct sequence in transmission step 741 via second air interface 91, second logical RLC connection 103 also being used for the transmission of the remaining packet data units containing useful data.

[0058] PDCP protocol unit 3100 in second superordinate network unit 55 initially ignores all packet data units received from mobile unit 10 which are not PDCP-SNPDUs.

[0059] Step 4:

[0060] After PDCP protocol unit 1100 of mobile unit 10 has received the PDCP-SNPDU from second superordinate network unit 55 according to transmission step 742, it initially stops the transfer of useful data to second superordinate network unit 55.

[0061] In the event that negotiated changes 720 relating to a connection change, such as re-setting of the internal protocol information, were agreed upon during the step-up of PDCP protocol unit 1100 of mobile unit 10, it now makes these changes 720.

[0062] PDCP protocol unit 1100 of mobile unit 10 subsequently sends the PDCP-downlink receive sequence number of the next packet data unit expected by it to PDCP protocol unit 3100 of second superordinate network unit 55, in that it generates a PDCP-SNPDU according to the table, sets the information element according to the PDCP-downlink receive sequence number, and hands over the PDCP-SNPDU according to transmission step 745 to identical RLC protocol unit 1200 of mobile unit 10, and thus to identical second logical RLC connection 103 for the error-free transmission in the proper sequence via second air interface 91 which is also used for the transmission of packet-data units transporting useful data. In this way, RLC protocol unit 1200 of mobile unit 10 transmits the PDCP-SNPDU to RLC protocol unit 3200 of second superordinate network unit 55 according to transmission step 746. RLC protocol unit 3200 of second superordinate network unit 55 then transmits the PDCP-SNPDU to PDCP protocol unit 3100 of second superordinate network unit 55 according to transmission step 747.

[0063] In addition, PDCP protocol unit 1100 of mobile unit 10 again initiates the transfer of useful data to second superordinate network unit 55, this useful-data transfer being begun and then continued accordingly with the packet data unit which was referenced by the received PDCP-uplink receive sequence number and which can be identified by a corresponding PDCP-uplink send sequence number assigned by PDCP protocol unit 1100 of mobile unit 10. In this context, the transmission, shown by way of example, of the first packet data unit after changes 720 in PDCP protocol unit 1100 of mobile unit 10 is carried out according to transmission step 750 initially from PDCP protocol unit 1100 of mobile unit 10 to RLC protocol unit 1200 of mobile unit 10, and from there, according to transmission step 755, to RLC protocol unit 3200 of second superordinate network unit 55, and from there, according to transmission step 758, to PDCP protocol unit 3100 of second superordinate network unit 55.

[0064] Step 5:

[0065] After PDCP protocol unit 3100 of second superordinate network unit 55 has received the PDCP-SNPDU from mobile unit 10 according to transmission step 747, it again initiates the transfer of useful data, this useful-data transfer being begun and then continued accordingly with the packet data unit which was referenced by the received PDCP-downlink receive sequence number and which can be identified by a corresponding PDCP-downlink send sequence number assigned-in PDCP protocol unit 3100 of second superordinate network unit 55.

[0066] PDCP protocol unit 3100 of second superordinate network unit 55 then sends the first packet data unit of this useful-data transfer via RLC protocol unit 3200 of second superordinate network unit 55 according to transmission step 760, and RLC protocol unit 1200 of mobile unit 10 according to transmission step 765, to PDCP protocol unit 1100 of mobile unit 10 according to transmission step 768, in that it hands over the packet data unit to identical RLC protocol unit 3200 of second superordinate network unit 55, and thus to the identical logical channel, namely, second logical RLC connection 103 for the error-free transmission in the proper sequence in transmission step 741 via second air interface 91. The further packet data units of the useful-data transfer are transmitted in corresponding manner between mobile unit 10 and second superordinate network unit 55.

[0067] Steps 1-5 are shown illustratively in FIG. 5. By way of example, a first message 705 from an RRC protocol unit 2000 of first superordinate network unit 50 to PDCP protocol unit 2100 of first superordinate network unit 50 is used for initiating third connection change 700, and thus for causing the transmission of transmission-specific information 730 to PDCP protocol unit 3100 of second superordinate network unit 55. A second message 708 from an RRC protocol unit 3000 of second superordinate network unit 55 to PDCP protocol unit 3100 of second superordinate network unit 55 is likewise used, by way of example, for initiating third connection change 700, and thus for causing the one initialization 710 of PDCP protocol unit 3100 of second superordinate network unit 55, after which transmission-specific information 730 may then be received.

[0068] The invention described makes it possible to efficiently carry out the necessary exchange of information via the next expected packet data unit in the form of the corresponding sequence numbers by way of the existing data channels without additional signaling and without setting up and tearing down new data channels or reconfiguring existing data channels.

[0069] The proposed data format for the PDCP-SNPDU generated for this by relevant PDCP protocol unit 1100, 3100 is very band-width efficient, since only a little unused information must be transmitted, namely, 5 bits, and apart from that, no more than the necessary information, namely, 8 bits for the corresponding sequence number and 3 bits for the corresponding PDU types, are present in the PDCP-SNPDU.

[0070] With the transmission of the PDCP receive sequence number by relevant PDCP protocol unit 1100, 3100 itself, after the respective transmission, the sequence numbers are in the protocol in which they are also evaluated. Thus, this invention does not lead to an internal data transfer from one protocol, e.g. the RRC protocol, to another.

[0071] The ignoring of received packet data units of the useful-data transfer by PDCP protocol unit 3100 of second superordinate network unit 55 from the moment of third connection change 700 to the moment of the reception of the PDCP-SNPDU in second superordinate network unit 55 with the aid of transmission step 747 ensures that no “old” packet data units, which were still treated prior to third connection change 700 by PDCP protocol unit 1100 of mobile unit 10, but were only received after third connection change 700 by PDCP protocol unit 3100 of second superordinate network unit 55, lead to errors in PDCP protocol unit 3100 of second superordinate network unit 55.

[0072] This has been achieved by the fact that the same RLC protocol units 1200, 3200, and thus the same second logical RLC connection 103, are used both for the transmission of packet data units for the useful-data transfer, and for the transmission of the PDCP-SNPDUs. Since the RLC protocol units provide for a transmission in the proper sequence of the data, after the reception of the PDCP-SNPDU, it is ensured that no “old” packet-data units can any longer be transmitted and given to higher protocol layers.

[0073] The resetting of PDCP protocol unit 1100 of mobile unit 10 only after reception of the PDCP-SNPDU from second superordinate network unit 55 in transmission step 742, but prior to the sending of the PDCP-SNPDU to second superordinate network unit 55 by transmission step 745, ensures that all “old” packet data units, which were still sent by first superordinate network unit 50, are decompressed with the old, not reset PDCP protocol unit 1100 of mobile unit 10, and all new packet data units which were sent by second superordinate network unit 55, are decompressed with reset PDCP protocol unit 1100 of mobile unit 10. 

What is claimed is:
 1. A method for operating a mobile radio network (1), in which useful data is transmitted between a mobile unit (10) and a first radio base station (25), the useful data being combined to form packet data units prior to its transmission; for the transmission of the packet data units, transmission-specific information which describes an instantaneous state of the transmission being stored both in the mobile unit (10) and in a first network unit (50) superordinate to the first radio base station (25), and in the event of a connection change of the mobile unit (10) from the first radio base station (25) to a second radio base station (30) having a second superordinate network unit (55), the transmission-specific information stored in the first superordinate network unit (50) is transmitted to the second superordinate network unit (55) in order to continue the transmission after the connection change essentially directly from its instantaneous state, wherein prior to the connection change, the transmission of the packet data units from the first radio base station (25) to the mobile unit (10) is halted by the first superordinate network unit (50); with the transmission-specific information from the first superordinate network unit (50), a first identifier of the packet data unit expected as next from the mobile unit (10) in the first superordinate network unit (50) is transmitted to the second superordinate network unit (55); and from the second superordinate network unit (55), a first connection-change packet data unit which includes the first identifier is transmitted to the mobile unit (10).
 2. The method as recited in claim 1, wherein the sending of packet data units is halted by the mobile unit (10) after receiving the first identifier.
 3. The method as recited in claim 1 or 2, wherein after reception of the first identifier, the mobile unit (10) transmits to the second superordinate network unit (55) a second connection-change packet data unit which includes a second identifier of the packet data unit expected as next from the second superordinate network unit (55) in the mobile unit (10).
 4. The method as recited in claim 3, wherein the second connection-change packet data unit is transmitted from the mobile unit (10) to the second superordinate network unit (55) after reconfiguration or resetting of the mobile unit (10).
 5. The method as recited in claim 3 or 4, wherein after reception of the second indicator, the sending of packet data units from the second superordinate network unit (55) to the mobile unit (10) is continued with the packet data unit referenced by the second indicator.
 5. The method as recited in claim 3, 4, or 5, wherein packet data units are ignored by the second superordinate network unit (55) which are received after the connection change and prior to receiving the second connection-change packet data unit from the mobile unit (10).
 6. The method as recited in one of claims 2 through 6, wherein after reception of the first indicator, the sending of packet data units from the mobile unit (10) is continued with the packet data unit referenced by the first indicator, it and the following packet data units being transmitted to the second superordinate network unit (55).
 8. The method as recited in claim 7, wherein after reconfiguration or resetting of the mobile unit (10), the sending of packet data units from the mobile unit (10) is continued with the packet data unit referenced by the first indicator, it and the following packet data units being transmitted to the second superordinate network unit (55).
 9. The method as recited in one of the preceding claims, wherein the second superordinate network unit (55) is initialized prior to reception of the transmission-specific information.
 10. The method as recited in one of the preceding claims, wherein the first identifier in the first connection-change packet data unit and/or the second identifier in the second connection-change packet data unit is in each case transmitted as the sequence number of the packet data unit expected as next.
 11. The method as recited in claim 10, wherein the sequence number is transmitted in a predefined format, particularly as an 8 bit value.
 12. The method as recited in claim 10 or 11, wherein the sequence number is transmitted in a connection-change packet data unit together with an information element which identifies the connection-change packet data unit as such. 